Emerging Artist of the Year Gregory Witt constructs an alternate universe of inscrutable devices.

Here is Gregory Witt in a nutshell: "I feel like I understand enough about the things around me to build them," Witt writes in his artist's statement. "So I have been."

Witt is a tinkerer. He finds a bunch of materials and assembles bizarre new machines. This is the concept behind Things That Float, an installation of automated artworks at Pittsburgh Center for the Arts. Each sculpture buzzes and hums, because the machines are always moving, day in, day out, performing their peculiar tasks. What do they do? Nothing practical. But form without function -- or no functional function, anyway -- seems to be the point.

One sculpture, "Refrigerator," looks like a trebuchet with a projector on one side and a tiny model refrigerator on the other. When the fridge's door automatically opens, the projector shines a picture of food into the interior. Then the refrigerator closes again, and there is only the blank white door. The repetition goes on -- open, shut, open, shut -- as if reminding us that this housebroken appliance is a machine, and that its use is endlessly repetitive.

For "Tree," Witt built an elaborate ramp that corkscrewed through a large tree. Using some kind of machine (we never see it), Witt sent a video camera traveling on the flat wooden track. In the resulting video, played on a small monitor, we get to ride around the bends, rise into the branches and ultimately fall off the ramp's edge, back to the ground. From a rider's point of view, it looks like a very slow rollercoaster. But it begs the questions: How did Witt send the camera around? And how did he keep it steady on such a flimsy-looking construct?

The exhibit marks Witt's selection as the PCA's Emerging Artist of the Year, a precocious honor for this recent graduate of Carnegie Mellon's MFA program. Things That Float shows off his peculiar sensibility -- both a talent for raw engineering, and a playful love of interchangeable parts. In Witt's world, devices don't need to accomplish anything. They only need to move around, stretch their limbs, make fun noises. If Dr. Seuss ever fiddled with an Erector Set, he might have built the prototypes for Witt's creations.

The largest sculpture is "Room," a gigantic assembly of gears made of drywall that slowly moves up and down. It would take a sharp machinist to sort out the ropes, cinderblocks and ladders that make it work, but the rest of us can marvel at its ineffable physics. There is a touch of mad science to Witt's work, and "Room" is by far the most ambitious apparatus.

When it comes to artists with rich technical skills, CMU has become a leader in the field. Alumni are always building high-concept installations, complete with video and electric engines and behaviors triggered by human movement. But there is something almost sweet about Witt and his machines. He seems like a guy who just likes to build stuff. Guided by such imagination, what impulse could be more pure?